Refer to figure.
=> (1) Calculate the endurance with landing gear retracted:

Note: Endurance is defined as the total time an aircraft can stay in flight until the tanks run dry.

6 000 kg ÷ 2 400 kg/h = 2.5 h

=> (2) Calculate the endurance with landing gear malfunction

Based on the flight planning data given, fuel consumption will increase by 180%.
Updated Fuel consumption: 2 400 kg/h + (180% x 2400 kg/hr) = 6720 kg/h

Endurance (with failure) = 6000 kg ÷ 6720 kg/h = 0.89 h

=> (3) The time penalty will be the difference between the original endurance time and the endurance with the landing gear malfunction:

2.5 h - 0.89 h = 1.61 h
1.61 h x 100% / 2.5 h = approx. 64.4 %

• Closest option: 65%